Loop driven vehicles

ABSTRACT

The specification discloses a motor cycle in which a power unit is mounted in a frame on resilient mountings and the rear road wheel is mounted in a fork swinging on the power unit and connected to springing means. There are two mounting means and a lateral locating means between the power unit and the frame, such mountings being at the apices of a triangle lying in a plane perpendicular to the rotary axis of the rear road wheel. The mounting means are resilient and the means together, are such as to allow a greater amplitude of movement in directions radial of said rotary axis than in directions parallel to said rotary axis and the movement of the power unit relative to the frame at each of said means is positively controlled in directions parallel to said axis. The specification also discloses that the mountings are located on parts of the frame which are rigidly interconnected with a link from one of the mountings to the power unit. The frame may be of sheet metal construction.

United States Patent [191 [111 3,783,961 Hooper 1 1 Jan. 8, 1974 LOOPDRIVEN VEHICLES Primary ExaminerKenneth I-l. Betts AssistantExaminerJohn P. Silverstrim [75] Inventor. lsifg'lrlixldidlglgpgz-lglpirdsley near ,Atmmey Kurt Kelman [73] Assignee: Norton VilliersLimited, [57] ABSTRACT Wolverhampton, England [22] Filed: July 2, 1971[21] Appl. N0.: V [301 Eoreig n Application Priority Data [52] US. Cl.180/33 A, 180/64 R, 248/3 [51] Int. Cl B60k 5/12 [58] Field of Search180/33 R, 33 A, 30, 180/31, 32; 280/281 [56] References Cited UNITEDSTATES PATENTS 3,542,146 11/1970 Hooper et al 180/64 R 3,508,765 4/1970Bauer et a1. 280/281 3,233,916 2/1966 Bowden 280/281 X 2,770,311 11/1956Kreidler 180/33 R 2,743,783 5/1956 Kreidler 180/33 R FOREIGN PATENTS ORAPPLICATIONS 941,111 3/1956 Germany 180/33 A 487,682 6/1938 GreatBritain 180/33 R 9,877 I 2/1915 Greatliritain The specificationdiscloses a motor cycle in which a power unit is mounted in a frame onresilient mountings and the rear road wheel is mounted in a forkswinging on the power unit and connected to springing means. There aretwo mounting means and a lateral locating means between the power unitand the frame, such mountings being at the apices of a triangle lying ina plane perpendicular to the rotary axis of the rear road wheel. Themounting means are resilient and the means together, are such as toallow a greater amplitude of movement in directions radial of saidrotary axis than in directions parallel to said rotary axis and themovement of the power unit relative to the frame at each of said meansis positively controlled in directions parallel to said axis. Thespecification also discloses that the mountings are located on parts ofthe frame which are rigidly interconnected with a link from one of themountings to the power unit. The frame may be of sheet metalconstruction.

PATENTED JAN 8 SHEET 2 OF 5 PATENTEU 8W4 SHEET 3 [1F 5 PATENTEBJAN 8I974SHEET LL BF 5 LOOP DRIVEN VEHICLES BACKGROUND OF THE INVENTION 1. Fieldof the Invention The invention is concerned with vehicles which aredriven by a flexible loop, particularly a chain, and the invention isapplicable to motor cycles including all steerable two wheeled powerdriven vehicles, and also to snowmobiles.

2. Description of the Prior Art In U.S. Pat. No. 3,542,146 which issuedon the 24th Nov. T9 70 on the application of Bernard Hooper and RobertVictor Trigg there is described a motor cycle construction in which thepower unit is mounted on the frame by three resilient mountings at theapices of a triangle lying in a plane perpendicular to the rotary axisof the driven road wheel.

In said patent we described how two of the resilient mountings eachincluded a shaft secured to the frame or the power unit and a tubularassembly secured to the power unit or the frame and a mass of resilientmaterial between the shaft and the tubular assembly, the shaft and thetubular assembly carrying abutments which through anti-friction washerslimited positively the movement of the power unit relative to the framein directions parallel to the said axis.

We disclosed how between the cylinder head and the frame there was amounting comprising resilient discs in compression in a directionperpendicular to their faces which were perpendicular to the rotary axisof the road wheel.

We have found that the suspension described in said patent is aconsiderable improvement over the prior art and locates the power unitrelative to the frame in a manner which is entirely suitable for highspeed touring motor cycles.

We have found surprisingly, however, that where one is dealing withextremely high performance racing motor cycles the performance of themotorcycle can be significantly increased by arranging each of themountings so that there is a positive limitation on the movement of thepower unit relative to the frame in directions parallel to the rotaryaxis of the road wheel.

When a racing motor cycle is cornering, the forces between the powerunit and the frame are very considerable and we have found that whilemovement of the power unit relative to the frame in directionsperpendicular to the rotary axis of the road wheel are acceptable,movement of the power unit relative to the frame in directions parallelto said axis must be positively controlled in extremely high performanceracing motor cycles.

SUMMARY OF THE INVENTION It is an object of the invention to provide avehicle driven by a flexible loop, particularly but not exclusively achain, in which the power unit is mounted in the frame in such a mannerthat forces tending to displace the power unit in directions parallel tothe rotary axis of the driven wheel are positively controlled.

It is another object of the invention to provide in a motor cycle thecombination of a power unit, a frame, and mountings between the powerunit and the frame which can withstand the extremly high forces whichoccur in very high speed racing motor cycles and can thereforesignificantly increase the speed of such motor cycles over a windingcourse, i.e., can decrease the time taken to circuit a winding course.

According to the invention 1 we provide a vehicle comprising a frame; apower unit movably mounted on the frame but having a neutral positionrelative thereto; a fork pivotally mounted on the power unit; a drivingwheel rotatably mounted in the fork; a driving loop interconnecting thedriving wheel and the power unit; and three mountings between the powerunit and the frame; the mountings being located respectively at theapices of a triangle lying in a plane perpendicular to the axis ofrotation of the driving wheel, each of the mountings comprising a firstrigid mounting element fixed to one of the power units andthe' frame, asecond rigid mounting element fixed to the other of the power units andthe frame, each element providing two oppositely directed faces, thefaces of the elements of each mounting being arranged in two pairs, eachpair comprising one face from each element with the faces of each pairfacing one another, and a thrust member of bearing material interposedbetween each pair of faces; each of at least two of the mountingsincluding a mass of resilient material interposed between the elements;the mountings controlling movement of the power unit relative to theframe so that the permitted amplitude of such movement in firstdirections radial to the axis is controlled by deformation of theresilient material and is a number of times greater than the permittedamplitude of such movement in second directions parallel to said axiswhich latter amplitude is.controlled by said bearing material.

BRIEF DESCRIPTION OF-THE DRAWINGS.

The invention will now be described in detail by way of example withreference to the accompanying drawings in which:

FIG. 1 is a perspective view of a motor cycle constuting a firstembodiment of the invention;

FIG. 2 is a cross-section through a first form of mounting for the powerunit of the motor cycle of FIG. 1;

FIG. 3 is a section through a lateral locating means for a power unit ofthe motor cycle of FIG. 1;

FIG. 4 is a partial section through a second type of mounting unit forthe motor cycle of FIG. 1;

FIG. 5 is a sectional view through a second type of lateral locatingmeans for the power unit of the motor cycle of FIG. 1; and

FIG. 6 is a perspective view of a motor cycle constituting a secondembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1 thisshows a motor cycle having a frame indicated generally at 10. The frameis in many respects similar to that described in US. Pat. No. 3,508,765issued the 28th Apr.- 1970 on the application of Stefan George Bauer,Bernard Hooper and Robert Victor Trigg. The main difference between theframe shown in FIG. 1 and that described in the above mentioned US. Pat.No. 3,508,765 is that in the former the tubes which were provided in theprevious arrangement to support the engine have been dispensed with andthe engine is supported solely from the rigid, triangulated frame.

It has been common in the past to have bent tubes in a tubular motorcycle frame and to have a least one of the power unit mountingssupported from said bent tubes as described in said patent. We havefound, however, that such bent tubes tend to deflect under extreme loadsand as a result there can be a disadvantageous effect on the motor cyclehandling, particularly where the swinging fork which carries the rearroad wheel is pivotally mounted on the power unit. The power unit maytwist about a vertical axis and thus allow the driven wheel to twistabout said axis thus affecting handling characteristics. As will bedescribed in detail below, the power unit of the present invention ispreferably mounted directly from the rigid part of the frame and thusnot rely for its location on any bent tubes.

The frame shown in FIG. 1 comprises a backbone 11 having a support 12 atits front end which pivotally supports the front fork 13 in which ismounted the front road wheel 14. Secured to the backbone 11approximately half way along the backbone are two straight tubes 15which at their upper ends are rigidly secured to the backbone throughbent portions 16 and gussets 17. The bent portions 16 and gussets 17form transversely extending rigid attachment means for the tubes 15 andproject on both sides of the backbone 11. It will be seen that the tubesare straight up to the gussets 17 and are thus rigidly connected to thebackbone 11 and cannot move relative thereto.

There is a second pair of tubes at the rear end of the backbone of whichone tube 18 is shown and is gusseted at its upper end at 19 to thebackbone and is thus rigidly secured to the backbone. The gussets 19form transversely extending rigid attachment means for the tubes 18 andproject on both sides of the backbone 11. On each side of the frame, thetubes 15 and 18 are joined at a junction 20. It will be appreciated,therefore, that the backbone l1 and the tubes 15 and 18 form a rigidtriangulated structure from which the power unit may be supported andthat there is no danger of this frame unit deflecting under extreme loadbecause of its triangulated construction. Further details of the preciseconstruction of the frame can be obtained from said US. Pat. No.3,508,765.

A power unit for the motor cycle is indicated generally at 21 and in theexample shown comprises a unitary engine and gearbox, the engine havinga cylinder block 22 carrying a carburettor 23 and an exhaust pipe 24.The rear road or driving wheel is indicated at 25 and is rotatablymounted about an axis 26 in a fork 27 which is pivotally mounted at 28to the power unit 21. The wheel 25 is drivingly connected with a powerunit through a chain 29 but this chain could be replaced by some otherform of driving loop such as an internally toothed belt. Conventionalspringing means 30 are interposed between the fork 27 and the frame 10.

The power unit is mounted on the frame by two mounting means ormountings indicated at 31 and 32 respectively and lateral locating means33. These means are located at the apices of a triangle lying in a planeperpendicular to the rotary axis 26 of the driving wheel 25. The laterallocating means 33 is connected to the power unit through a rigid link 34which is at its lower end rigidly connected to the power unit. By theuse of such a link, both of the means 31 and 33 can be anchored to thebackbone 11 while the mounting means 32 is anchored to the frameadjacent to the junctions 20 so that each of the three means is rigidlylocated relative to the other two means on the rigid frame and it willbe seen that no bent tubes are used to locate or support the engine asis described in said US. Pat. No. 3,542,146.

The construction of the means 31, 32 and 33 will now be described.

Referring now to FIG. 2, this shows the mounting 31. It comprises anelement in the form of a tubular assembly 35 comprising a mountingsleeve 36 which is welded to plates 37 which in turn are welded to thebackbone 11. At each end, the mounting sleeve 35 carries thrust plates38 which provide outwardly directed faces 39.

A bracket is secured to the cylinder block 22 and comprises two plates40 between which is secured a shaft 41. The shaft 41 carries thrustplates 42 and these thrust plates provide inwardly directed surfaces 43.Be tween each pair of surfaces 39 and 43 is interposed a washer ofbearing material 44. Seals 45 seal the ends of the tubular assembly.

Bushes 46 of resilient material are interposed between the shaft 41 andthe tubular assembly 36 and each bush of resilient material is bonded toinner and outer metal sleeves which engage the shaft 41 and mountingsleeve 36 respectively. Two further resilient bushes 47 are providedsurrounding the shaft of lesser diameter than the bushes 46. It will benoted that the longitudinal axis of the shaft 41 is parallel to therotary axis 26 of the driving wheel 25.

The lateral locating means 33 is similar to the mounting 31 except thatit is shorter and does not have the resilient bushes such as 46 and 47.Thus the means 33 comprises plates 48 which are welded to the backbone11 and which carry a mounting sleeve 49 forming part ofa tubularassembly 50. The tubular assembly also includes thrust plates 51 whichhave outwardly directed surfaces 52. The link 34 comprises spaced lugs53 between which extends a shaft 54 carrying nuts 55 at its ends. Theshaft 54 carries thrust plates 56 and these thrust plates provideinwardly directed faces 57. Between each pair of faces 52 and 57 is awasher 58 of bearing material. Seals 59 seal the ends of the means.

The mounting 32 is in all respects similar to the mounting 31 and isinterposed between the power unit and the junctions 20 of the tubes 15and 18.

Movement of the power unit in the frame in directions perpendicular tothe rotary axis 26 is controlled by compression of the resilient bushes46 in the mountings 31 and 32 and, under extreme deflections, by thecompression of the bushes 47. Movement of the power unit 21 parallel tothe rotary axis 26 is controlled by the clearance between each pair ofopposed faces on the means such as 39 and 43 for the mountings 31 and 32and the faces 52 and 57 for the lateral locating means 33 and the washer44 or 58 of bearing'material between each opposed pair of faces. Themovement of the power unit relative to the frame in directions parallelto the axis 26 is thus limited positively by the engagement of the facesof each opposed pair with the washer of bearing material between thefaces of the pair. This positive limitation on movement of the powerunit parallel to the axis 26, therefore, locates the power unitpositively in this direction. The amplitude of the permitted movement ofthe power unit in directions parallel to the axis 26 is a number oftimes less than the amplitude of the permitted movement in directionsperpendicular to the axis, such movements perpendicular to the axisbeing controlled by the compression of the resilient bushes 46 and 47.In other words, the power unit can oscillate substantially in planesperpendicular to the axis 26 with a relatively high amplitude and thisdoes not affect the handling characteristics of the motor cycle but thepower unit has a relatively lower permitted amplitude of movement indirections parallel to the axis 26 since such movement does adverselyaffect the handling characteristics of the motor cycle due to the factthat the driving wheel is mounted on the power unit 21.

Referring now to FIG. 4 this shows in part a modification of themounting 31. The modified mounting comprises a tubular assemblyindicated generally at and comprising a mounting sleeve 61 which at itsends carries thrust plates 62, the thrust plates providing outwardlydirected surfaces 63. A shaft 64 passes through the tubular assembly andcarries thrust plates 65 having inwardly directed surfaces 66. The shaftis secured to the frame or power unit through plates 67 and the mountingsleeve 61 is secured to the other of the frame or the power unit throughmounting plates not shown. The shaft 64 carries resilient bushes 68which operate in the same manner as the bushes 46 in FIG. 2. Interposedbetween each pair of faces 63 and 66 there is a block of resilientpolyurethane material 69 which had been compressed between the faces 63and 69 so that it is substantially solid in directions perpendicular tosaid faces thus positively locating the tubular assembly 60 and theshaft 64 relative to one another in directions parallel to thelongitudinal axis of the shaft 64 i.e. parallel to the rotary axis 26 ofthe rear road wheel. The block of material 69 has a plurality ofradially directed holes 70 therein. It is known that when a resilientmaterial is compressed strongly in one direction then the capacity ofthe material to resist shear stresses in a perpendicular direction isreduced..Thus the blocks 69 have the property of limiting virtuallypositively the endwise movement of the shaft 64 relative to the mountingsleeve 61 while allowing relative movement of the shaft 64 within thesleeve 61 in radial directions. The resulting structure thereforefunctions substantially as does the structure of the mounting 31.

The mountings 31 and 32 may be replaced with mountings modified asdescribed in relation to FIG. 4 and the lateral locating means 33 may beas described in relation to FIG. 3 except that blocks of resilientmaterial such as 69 take the place of the washers '58.

FIG. 5 illustrates a modification of the lateral locating means 33 and,referring to that Figure, the backbone 11 carries a bracket 71 havingparallel faces 72. The upper end of a link similar to the link 34 isindicated at 73 and bolted to the end of the link are plates 74 whichcarry pads 75 of nylon or similar material having faces 76 which areparallel to, and slightly spaced from, the faces 72.

It will be seen that the lateral locating means of FIG. 5 controlsmovement of the power unit in directions parallel to the axis 26 withoutrestraining movement in directions perpendicular to the axis.

FIG. 6 shows a motor cycle similar to that of FIG. 1 except that inplace of the triangulated frame 10 there is a sheet metal frameindicated generally at 77. Thus this frame carries front forks 78 withthe front road wheel 79 and also the power unit 80 which in turn carriesthe rear road wheel 81 through a pivoted fork 82, the wheel being drivenby a chain 83. The power unit 80 is mounted on the frame by two mounting84 and 85 and lateral locating means 86. The mountings 84 and 85 are ofthe construction described in relation to FIG. 2 and the laterallocating means 86is of the construction describedin relation to FIG. 3.A link 87 extends from the means 86 and is rigidly secured to the powerunit 80.

The frame is generally of box construction, having an upper part 88,side plates 89 and front and rear plates 90 and 91. It will thus be seenthat the frame is substantially in the form of a box girder and the link87 passes into the box girder frame and is secured to a bracket 92provided therein. Since the frame is of box girder construction, thepoints at which the means 84, 85 and 86 are secured are rigidlyinterconnected and therefore cannot move relative to one another. evenin extreme stress so that even with a very high speed racing motor cyclethe attachment points of the means 84, 85 and 86 to the frame do notmove relative to one another under stress and thus the handling of themotor cycle is improved.

We have found that by positively limiting the movement of the power unitrelative to the frame in directions parallel to the axis 26 at all threemeans, very advantageous results are obtained and that these results areimproved further where, as is preferred, the mountings are located on atriangulated tubular frame as described in FIG. 1 or a box section sheetmetal frame as described in relation to FIG. 5 and the means areprevented from moving relative to one another under. the extremestresses which occur during the operation of high speed racing motorcycles.

The invention has been specifically described in relation to motorcycles but it may also be applied to other two wheeled steerablevehicles and the engine mounting systems described could also be appliedto snowmobiles in which case the driven wheel 81 would drive the trackof the snowmobile.

I claim:

1. A vehicle comprising: a frame, a power unit movably mounted on theframe but having a neutral position relative thereto; a fork pivotallymounted on the power unit; a driving, wheel rotatably mounted in thefork;a driving loop interconnecting the driving wheel and the powerunit; and means for mounting the power unit to the frame comprising twomounting means and one lateral locating means interposed between thepower unit and the frame; said means for mounting being locatedrespectively at the apices of a triangle lying in a plane perpendicularto the axis of rotation of the driving wheel, each of said means formounting comprising a first rigid mounting element fixed to one of thepower unit and the frame, a second rigid mounting element fixed to theother of the power unit and the frame, each of said mounting elementsproviding two oppositely directed faces, said faces of said mountingelements of each of said means for mounting being arranged in two pairs,each said pair comprising one said face from each said mounting elementwith said faces of each said pair facing one another, and a thrustmember of bearing material interposed between said faces of each saidpair; each of said mounting means including a mass of resilient materialinterposed between said mounting elements thereof and located' so as toprovide substantially the sole support for the weight of the power unitand so as to control movement of the power unit relative to the frame infirst directions radial to said axis of rotation by deformation of theresilient material; each of said means for mounting positivelycontrolling said movement in second directions parallel to said axis ofrotation by engagement between said faces and said thrust members whichare substantially incompressible in said second directions, thepermitted amplitude of said movement in said first directions being anumber of times greater than the permitted amplitude of said movement insaid second directions, said lateral locating means being at an upperapex of said triangle and serving to control said movement of the powerunit solely in said second directions.

2. A vehicle according to claim 1 wherein said first rigid mountingelement of each of said mounting means is in the form of a tubularassembly having said oppositely directed faces at the ends thereof;wherein said second rigid mounting element of each of said mountingmeans is in the form of a shaft passing through said tubular assemblyand carrying abutment plates at the ends thereof; which plates providesaid oppositely directed faces of the second rigid mounting element, andwherein the mass of resilient material of each said mounting means is inthe form of bush means within the tubular assembly and surrounding theshaft.

3. A vehicle according to claim 2 wherein each said thrust member ofeach of said two mounting means is received with clearance between thefaces of each said pair of said faces of said mounting means.

4. A vehicle according to claim 2 wherein each said thrust member ofeach of said two mounting means comprises a block of resilient materialcompressed between each said pair of said facesof said mounting means indirections parallel to the longitudinal axis of the tubular assembly,the resilient material of said block being compressed to such an extentas positively to limit movement of the power unit relative to the framein said second directions.

5. A vehicle according to claim 2 wherein said first rigid mountingelement of said lateral locating means is in the form of a tubularassembly having said oppositely directed faces at the ends thereof; andwherein the second rigid mounting element of said lateral locating meansis in the form of a shaft passing freely through said tubular assemblywith clearance and carrying abutment plates at the ends thereof, whichplates provide said oppositely directed faces of said second rigidmounting element.

6. A vehicle according to claim 5 wherein each said thrust member ofsaid lateral locating means comprises a block of resilient materialcompressed between each said pair of said faces of said lateral locatingmeans in a direction parallel to the longitudinal axis of the tubularassembly, the resilient material of the block being compressed to suchextent as positively to limit movement of the power unit relative to theframe in said second directions.

7. A vehicle according to claim 5 wherein each said thrust member ofsaid lateral locating means is received with clearance between the facesof each said pair of said faces of said lateral locating means.

8. A vehicle according to claim 2 wherein said rigid mounting elementsof said lateral locating means are both of U-shape, the limbs of the Uof one said rigid mounting element being parallel to the limbs of the Uof the other said rigid mounting element, said limbs providing saidfaces of said rigid mounting elements between which said bearingmaterial is interposed.

9. A vehicle according to claim 1 wherein the frame includes a straighttubular backbone having front and rear ends, first and secondtransversely extending rigid attachment means secured to said backboneadjacent its rear end and intermediate its ends respectively, said rigidattachment means projecting on both sides of said backbone, a first pairof spaced-apart substantially parallel tubes extending generallydownwardly from, and secured to, said first rigid attachment means and asecond pair of spaced-apart substantially parallel tubes inclinedrelative to said backbone and extending rearwardly from, and secured to,said second rigid attachment means, said tubes of each said pair beingarranged one on either side of said backbone, said tubes lying to oneside of the backbone being joined and said tubes lying to the other sideof the backbone being joined, all said tubes being straight betweentheir junctions and said rigid attachment means, one said mountingelement of each of said means for mounting being secured to the frame,said one mounting element of one of said means for mounting beingsecured to the backbone, and said one mounting element of one of saidtwo mounting means being secured to the frame adjacent to the tubejunctions.

10. A vehicle according to claim 9 wherein said one mounting element ofthe lateral locating means is secured to the backbone and said othermounting element of said lateral locating means is connected to a linkrigidly secured to the power unit.

11. A vehicle according to claim 1 wherein the vehicle comprises a rigidsheet metal frame and one of said mounting elements of each of saidmeans for mounting is secured to a different part of the frame, whichparts are rigidly interconnected by the frame.

12. A vehicle according to claim 11 wherein one of said mountingelements of said lateral locating means is secured to a rigid linkrigidly connected to the power umt.

1. A vehicle comprising: a frame, a power unit movably mounted on theframe but having a neutral position relative thereto; a fork pivotallymounted on the power unit; a driving wheel rotatably mounted in thefork; a driving loop interconnecting the driving wheel and the powerunit; and means for mounting the power unit to the frame comprising twomounting means and one lateral locating means interposed between thepower unit and the frame; said means for mounting being locatedrespectively at the apices of a triangle lying in a plane perpendicularto the axis of rotation of the driving wheel, each of said means formounting comprising a first rigid mounting element fixed to one of thepower unit and the frame, a second rigid mounting element fixed to theother of the power unit and the frame, each of said mounting elementsproviding two oppositely directed faces, said faces of said mountingelements of each of said means for mounting being arranged in two pairs,each said pair comprising one said face from each said mounting elementwith said faces of each said pair facing one another, and a thrustmember of bearing material interposed between said faces of each saidpair; each of said mounting means including a mass of resilient materialinterposed between said mounting elements thereof and located so as toprovide substantially the sole support for the weight of the power unitand so as to control movement of the power unit relative to the frame infirst directions radial to said axis of rotation by deformation of theresilient material; each of said means for mounting positivelycontrolling said movement in second directions parallel to said axis ofrotation by engagement between said faces and said thrust members whichare substantially incompressible in said second directions, thepermitted amplitude of said movement in said first directions being anumber of times greater than the permitted amplitude of said movement insaid second directions, said lateral locating means being at an upperapex of said triangle and serving to control said movement of the powerunit solely in said second directions.
 2. A vehicle according to claim 1wherein said first rigid mounting element of each of said mounting meansis in the form of a tubular assembly having said oppositely directedfaces at the ends thereof; wherein said second rigid mounting element ofeach of said mounting means is in the form of a shaft passing throughsaid tubular assembly and carrying abutment plates at the ends thereof;which plates provide said oppositely directed faces of the second rigidmounting element, and wherein the mass of resilient material of eachsaid mounting means is in the form of bush means within the tubularassembly and surrounding the shaft.
 3. A vehicle according to claim 2wherein each said thrust member of each of said two mounting means isreceived with clearance between the faces of each said pair of saidfaces of said mounting means.
 4. A vehicle according to claim 2 whereineach said thrust member of each of said two mounting means comprises ablock of resilient material compressed between each said pair of saidfaces of said mounting means in directions parallel to the longitudinalaxis of the tubular assembly, the resilient material of said block beingcompressed to such an extent as positively to limit movement of thepower unit relative to the frame in said second directions.
 5. A vehicleaccording to claim 2 wherein said first rigid mounting element of saidlatEral locating means is in the form of a tubular assembly having saidoppositely directed faces at the ends thereof; and wherein the secondrigid mounting element of said lateral locating means is in the form ofa shaft passing freely through said tubular assembly with clearance andcarrying abutment plates at the ends thereof, which plates provide saidoppositely directed faces of said second rigid mounting element.
 6. Avehicle according to claim 5 wherein each said thrust member of saidlateral locating means comprises a block of resilient materialcompressed between each said pair of said faces of said lateral locatingmeans in a direction parallel to the longitudinal axis of the tubularassembly, the resilient material of the block being compressed to suchextent as positively to limit movement of the power unit relative to theframe in said second directions.
 7. A vehicle according to claim 5wherein each said thrust member of said lateral locating means isreceived with clearance between the faces of each said pair of saidfaces of said lateral locating means.
 8. A vehicle according to claim 2wherein said rigid mounting elements of said lateral locating means areboth of U-shape, the limbs of the U of one said rigid mounting elementbeing parallel to the limbs of the U of the other said rigid mountingelement, said limbs providing said faces of said rigid mounting elementsbetween which said bearing material is interposed.
 9. A vehicleaccording to claim 1 wherein the frame includes a straight tubularbackbone having front and rear ends, first and second transverselyextending rigid attachment means secured to said backbone adjacent itsrear end and intermediate its ends respectively, said rigid attachmentmeans projecting on both sides of said backbone, a first pair ofspaced-apart substantially parallel tubes extending generally downwardlyfrom, and secured to, said first rigid attachment means and a secondpair of spaced-apart substantially parallel tubes inclined relative tosaid backbone and extending rearwardly from, and secured to, said secondrigid attachment means, said tubes of each said pair being arranged oneon either side of said backbone, said tubes lying to one side of thebackbone being joined and said tubes lying to the other side of thebackbone being joined, all said tubes being straight between theirjunctions and said rigid attachment means, one said mounting element ofeach of said means for mounting being secured to the frame, said onemounting element of one of said means for mounting being secured to thebackbone, and said one mounting element of one of said two mountingmeans being secured to the frame adjacent to the tube junctions.
 10. Avehicle according to claim 9 wherein said one mounting element of thelateral locating means is secured to the backbone and said othermounting element of said lateral locating means is connected to a linkrigidly secured to the power unit.
 11. A vehicle according to claim 1wherein the vehicle comprises a rigid sheet metal frame and one of saidmounting elements of each of said means for mounting is secured to adifferent part of the frame, which parts are rigidly interconnected bythe frame.
 12. A vehicle according to claim 11 wherein one of saidmounting elements of said lateral locating means is secured to a rigidlink rigidly connected to the power unit.